1. Field of the Invention
The present invention relates, in general, to a phase-shifting photomask blank and a method of manufacturing the same as well as a phase-shifting photomask. It relates, in particular, to an attenuation type of phase-shifting photomask blank in which the light of exposure wavelength is attenuated and which is particularly suitable to an exposure by an ultraviolet light such as KrF excimer laser or the like, and a method of manufacturing the same as well as a phase-shifting photomask.
2. Description of the Related Art
In a phase-shifting photomask 208 as shown in FIG. 18B there is formed a circuit pattern, i.e., a phase-shifting pattern 230 which is to be transferred to a semiconductor substrate, in the following manner. Namely, a desired portion of a phase-shifting film 204 on the surface of a phase-shifting photomask blank 200 shown in FIG. 18A is etched. An opening portion 210 in which the surface of a quartz substrate 201 is exposed and a phase-shifting portion 205 made up of a phase-shifting film that has been left unetched constitute the circuit pattern to be transferred to the semiconductor substrate.
This phase-shifting portion 205 has a translucency at a wavelength of the exposure light. The thickness of this phase-shifting portion 205 is arranged such that the phase between the exposure light 206 penetrating the above-described opening portion 210 and the exposure light penetrating the above-described phase-shifting portion 205 differs by 180.degree. (degrees). Therefore, when a wafer as shown in FIG. 18C is exposed, the optical intensity on the wafer in the border between the opening portion 210 and the phase-shifting portion 205 becomes zero. As a consequence, the circuit pattern transferred by the phase-shifting photomask has a high resolution.
As the above-described phase-shifting film 204 a single-layer film and a multi-layer film are normally used. The transmittance of the exposure light in the phase-shifting portion 205 is required to be normally about 3-40% in order to obtain an adequate amount of exposure light in lithography as well as to adjust the resist film thickness after developing of a resist film coated on the wafer.
However, in case the phase-shifting film 204 is constituted or made by the multi-layer film according to the prior art, there is a disadvantage in that the transmittance of the exposure light of short wavelength is low. In case KrF excimer laser (wavelength: 248 nm) is used as the exposure light to improve the resolution, there is a disadvantage in that a sufficient exposure cannot be made in the phase-shifting photomask made up of multiple layers.
On the other hand, in case the phase-shifting film is constituted by a single-layer film, the following method is conventionally used. Namely, a target of molybdenum silicide is sputtered in an atmosphere consisting of argon and oxygen, argon, oxygen and nitrogen, or argon and nitrous oxide (Ar: 84-72%, N.sub.2 O: 16-28%) (see Japanese Published Unexamined Patent Application No. 332152/1994) to thereby form a thin film of an oxide or a nitrided oxide (or an oxynitride) of molybdenum silicide on the quartz substrate 201. This method, however, has a disadvantage in that, though the light transmittance is high, the resistance to attack by chemical agents (chemical durability) of the product is poor.
Furthermore, in case the single-layer film is an oxide film, the internal stress in the film is large. Therefore, there is a disadvantage in that the film is peeled off from the substrate or that the substrate is deformed.
Still furthermore, the single-layer film of the oxide or nitrided-oxide of molybdenum silicide exceeds about 50% in transmittance at a wavelength (e.g., .lambda.=488 nm) to be normally used in defect inspection of photomasks. Therefore, there is a serious disadvantage in that the defect inspection is difficult.